The invention relates to an electric display device for a vehicle, particularly a motor vehicle, with at least one indicating instrument, with a memory which stores at least one desired display value to which the display means can be set in testing mode, and with switch means for the switchable division of pulses of a variable to be indicated, particularly a speed of rotation.
Such electric display devices can be developed with liquid crystals in order to produce all display functions of a so-called combination instrument for an automotive vehicle. The combination instrument may comprise digital speed display means as well as quasi-analog rpm display means in addition to segments for warning fields, symbols, units and legends.
The display means are controlled by a microcomputer to which measurement variables such as rpm, distance increments, oil pressure, temperature and tank level are fed via converters or pulse-forming means. The microcomputer converts the measurement variables into segment displays, in particular into digits and quasi-analog displays.
In order to make certain that the display means are able to display the measurement variables properly when the vehicle is in operation, a so-called testing mode is called up, in the case of an electric display device, before the operating of the vehicle and, in particular, directly after the turning on of the ignition, which mode, due to the programming of the microcomputer, can proceed automatically.
This is done in the manner that the quasi-analog display means, such as speed of rotation and tank level, increment, starting from a minimum display value, to the maximum value and remain there for some time. On the other hand, with the digital speed display means, characteristic successions of digits are displayed in the testing mode, including a sequence of digits by which the segments are covered as completely as possible.
This testing mode proceeds automatically during the test phase when the ignition is turned on. The display means is then switched to normal operation for display of the actual measured variables. This switching can, however, also take place already during the test phase so that, for instance, the driver of the vehicle can be advised of the operating conditions upon starting. This premature external switching can be produced by a signal from the oil pressure, the generator, the starter, or the ignition terminal of the ignition coil.
By switching, such indicating means can be adapted to different types of vehicles and engines. In particular, adaptation of the measurement of the speed of rotation to the number of cylinders of the engine is necessary if the ignition pulses are evaluated. For this purpose, there is provided in a microcomputer, a programmable divider which, before the processing of the rpm pulses, reduces them depending on the number of cylinders. Another adaptation can be conceivable for the so-called Vehicle W Constant*, by which the distance-increment pulses are adapted to the gear transmission ratio. For the switching of the display device, a switch can be provided which, before the installation of the display device, is brought into a position which corresponds to the pertinent, in part varying, vehicle parameters. One could conceive of pasting a legend on the display device for the important verification of the adapted setting or tearing it off from same or else stamping a control tag. These processes are, however, at least time consuming. Furthermore, as a result of these measures, and in particular in the case of retrofitting of the vehicle in a workshop, erroneous adaptations can occur. FNT *The number of revolutions of the crank shaft in the highest gear upon movement of the vehicle over a distance of 100 m.
The present invention, therefore, has the object of so developing an electric display device of the aforementioned type that the correct adjustment of the display device can be checked with increased certainty upon the final verification. The pasting on or tearing off of a legend or the stamping of a control tag ought to be expendable in order to save time. A retrofitting in the workshop should be particularly installation-reliable.